Visceral sensory neurons of the vagus and glossopharyngeal nerves innervate the major organ systems of the thorax and abdomen. These afferent neurons transmit information concerning such diverse stimuli as blood pressure, gastric distention, bronchiolar irritation and blood oxygenation to the CNS. The objective of this project is to define the chemical neuroanatomy of these visceral sensory neurons which are located in the nodose and petrosal ganglia. This includes studies of neurotransmitters, their distribution and correlation with CNS and peripheral projections, neurotransmitter co-existence, and the regulation of transmitter content and expression. Our current hypothesis proposes that visceral sensory neurons of the nodose and petrosal ganglia use multiple neurotransmitters and combinations of co-existence transmitters, and that the expression of transmitter in individual neurons is dependent upon the level of neuronal activity, and upon the target organ of innervation. Evidence for or against this hypothesis will be obtained by studying transmitter co-existence in the nodose and petrosal ganglia, determining patterns of co- existence in relation to the organ of innervation, localizing mRNA which encodes for precursors of the neurotransmitters, and subsequently determining whether changes in transmitter content or mRNA levels occur in visceral afferent neurons following changes in neuronal activity of connectivity. The techniques used in these studies include: immunocytochemistry retrograde tracing techniques, in situ hybridization histochemistry, neurotransmitter assays, and in vivo pharmacological approaches. These studies will provide information on the cellular neurobiology of transmitter systems in visceral sensory neurons which will be useful in the understanding and treatment of derangements of the autonomic control of the cardiovascular, respiratory, and gastrointestinal systems.